1. Field of the Invention
Polyurethane foams are used in numerous applications in the furniture and automotive industries. Flexible polyurethane foams suitable for cushioning applications require good load bearing properties while retaining good processing features.
2. Description of the Prior Art
Approaches taken to producing polyurethanes, particularly in the field of high resiliency foams with improved load-bearing properties, include using a styrene-acrylonitrile copolymer polyol to provide additional chain branching which contributes to higher load bearing. A second approach to achieving crosslinking necessary for desired load bearing properties involves the use of isocyanate prepolymers with large amounts of free isocyanate groups with regular polyisocyanates. The first two approaches employ higher cost reactants for the foaming formulation as compared with conventional polyols and polyisocyanates as well as requiring special storage conditions to prevent contamination of other materials. A third approach, and the most commonly tried, is to use low molecular weight amines and hydroxyl containing compounds as crosslinking compounds. Arylene diamines such as those taught in U.S. Pat. No. 3,644,235 are known to increase the load bearing properties of flexible polyurethane foams. Use of arylene diamines such as, for example, 4,4'-methylene-bis-(2-chloroaniline) is declining because of their suspected carcinogenic behavior. The use of carboxylic acid salts of hexamethylene diamine or aromatic diminishes as curing agents is taught in U.S. Pat. Nos. 3,478,089 and 3,511,814.